1. Field
The following description relates to a semiconductor device and a method of manufacturing the same, and to a metal-oxide-semiconductor field-effect transistor (MOSFET) having a halo region separately formed in a channel region located between a source LDD region and a drain LDD region.
2. Description of Related Art
High integration of semiconductor devices demands narrower intervals to be provided between a source and a drain of a transistor, which results in a shorter channel length and a shorter gate length. The structural limitation causes deterioration in the operation of semiconductor devices due to short-channel effects and hot carrier effects.
Various methods have been suggested to the structure of such semiconductor devices in order to ameliorate or eliminate the above-mentioned limitations and to obtain a better design for semiconductor devices to meet the target specifications of device characteristics. One of the methods is the formation of a lightly doped drain (LDD) structure. An LDD structure is a widely known solution to the above-mentioned limitations, and is thus used widely in the manufacture of semiconductor devices.
An LDD region of a MOSFET is formed by implanting a lower dose of impurity ions (N− for NMOS, P− for PMOS) than the dose implanted to form a source or a drain of the MOSFET. The LDD region is located between the source or drain junction region (N+ for NMOS, P+ for PMOS) and the channel region under a gate electrode.
Although the LDD region can reduce strong peak field due to excessively-doped drain, the LDD region introduces a series resistance, which in turn results in another limitation that results in the deterioration of semiconductor device performance.
The impurities within the source or drain junction region may diffuse to the channel region below the gate electrode when the impurities are heat-treated during the manufacturing process. Thus, a halo region that surrounds the LDD region may be formed so as to prevent the diffusion of impurities to the channel region below the gate electrode. While the addition of a halo region can reduce short-channel effects that are mainly caused by the decreasing channel length, the addition of the halo region can also cause the performance degradation of a MOSFET. For example, the addition of the halo region can reduce drain saturation current. However, the hot carrier reliability may be low.
As mentioned above, the MOSFET channel length may be reduced down to deep sub-micron level due to improved semiconductor device integration techniques. However, this also causes various short-channel effects that have not been witnessed in the conventional long channel devices. The short-channel effects are the main cause of limitations such as low breakdown voltage due to punch-through, reduced threshold voltage, increased leakage current, and hot-carrier effect.
Among the short-channel effects, deteriorations due to hot carrier are serious concern. The hot-carrier effects include the increase of substrate current and the shift in the drain saturation current, as well as the reduction of trans-conductance. The lifetime of the device may be also shortened.
Accordingly, it is necessary to effectively control the hot carrier effects of a semiconductor device, and a structural improvement of the semiconductor device is desirable. The structural shortcoming may also result in complicated manufacture process that increases the cost of production.